As its prior art, Patent Document 1 discloses a technology of this kind, for example. In this prior art, the pump control apparatus is formed of three variable displacement hydraulic pumps driven by one prime mover and of a plurality of actuators. The displacement volumes of the first and second hydraulic pumps are controlled on the basis of the self-discharge pressures P1 and P2 of these hydraulic pumps and the pressure P3′ into which the discharge pressure P3 of the third hydraulic pump is reduced by a pressure reducing valve. When the discharge pressure P3′ of the third hydraulic pump is high, the input torques of the first and second hydraulic pumps are controlled to be suppressed. In addition, the displacement volume of the third hydraulic pump is designed to be controlled only by the self-discharge pressure P3. The above mechanism can ensure a stable flow rate of the pressurized oil discharged from the third hydraulic pump without being influenced by fluctuations in the discharge flow rates of the first and second hydraulic pumps, or fluctuations in consumption torque. Further, the sum of the input torques of the first, second, and third hydraulic pumps is controlled not to exceed the available maximum power of the engine, whereby an overload on the engine can be prevented.
Patent document 1: JP, A 2002-242904